Pharmacodynamic interaction between oestradiol and adrenaline on intravascular aggregation induced by adenosine diphosphate in the rat.

Physiological levels of oestradiol and adrenaline inhibit intravascular aggregation of platelets, and effect dependent on the presence of an adrenal gland secretion (possibly adrenaline) and oestrogens, respectively. This infers a "mutual dependence" phenomenon. Acute adrenalectomy had a biphasic effect on intravascular aggregation: enhancing platelet aggregation when levels of oestradiol are high, e.g. in pro-oestrous rat, and reducing platelet aggregation when levels of oestradiol are nil or very low, i.e., in ovariectomized or di-oestrous rats, respectively. Ovariectomy also had a biphasic effect on platelet aggregation reducing aggregation in the absence of adrenaline and enhancing aggregation in its presence. Removal of endogenous oestradiol (by ovariectomy) and its replacement fully corroborates the "mutual dependence" hypothesis, whereas the removal of endogenous adrenaline (by acute adrenalectomy) and its replacement only partially supports it. It is concluded that, though both oestradiol and adrenaline have inhibitory effects on intravascular aggregation at physiological doses, each seems to need the full compliment of the other to achieve the effect.